Institute of Medical Engineering, University of Luebeck, Ratzeburger Allee 160, 23562 Luebeck, Germany.
Phys Med Biol. 2020 Sep 30;65(19):195014. doi: 10.1088/1361-6560/ab7e7e.
Magnetic particle imaging (MPI) is a new medical imaging technique visualizing the concentration distribution of superparamagnetic nanoparticles used as tracer material. MPI is not yet in clinical routine, since one of the challenges is the upscaling of scanners. Typically, the magnetic fields of MPI scanners are generated electromagnetically, resulting in an immense power consumption but providing high flexibility in terms of adjusting the field strengths and very fast image acquisition rates. Permanent magnets provide high flux densities and do not need any power supply. However, the flux density is not adjustable, and a mechanical movement is slow compared to electromagnetically varying fields. The MPI scanner concept proposed here uses permanent magnets and provides high flexibility, with the possibility to choose between fast overview scanning and detailed image acquisition. By mechanical rotation of magnetic rings in Halbach array configuration, it is possible to adjust the field or gradient strengths. The latter allows for determining the spatial resolution and the size of the field of view. A continuous mechanical rotation defines the coarseness of the scanning trajectory and image acquisition rate. This concept provides a comparable flexibility, as an alternating magnetic field and an adjustable field gradient can be applied as known from electromagnetically driven MPI systems, and therefore yields high potential for an enlarged system. We present the idea of an arrangement of Halbach arrays and how to calculate the generated magnetic fields. Simulations for an exemplary geometry are provided to show the potential of the proposed setup.
磁共振成像（MPI）是一种新的医学成像技术，可用于可视化超顺磁纳米粒子的浓度分布，这些纳米粒子可用作示踪剂。MPI 尚未在临床常规中使用，因为其中一个挑战是扫描仪的扩展。通常，MPI 扫描仪的磁场是通过电磁产生的，这导致了巨大的功耗，但在调整场强和非常快速的图像采集率方面提供了很高的灵活性。永磁体提供高磁通密度，不需要任何电源。然而，磁通密度不可调，与电磁变化的磁场相比，机械运动速度较慢。这里提出的 MPI 扫描仪概念使用永磁体，并提供了很高的灵活性，可以在快速全景扫描和详细图像采集之间进行选择。通过在 Halbach 阵列配置中机械旋转磁环，可以调整磁场或梯度强度。后者可以确定空间分辨率和视野大小。连续的机械旋转定义了扫描轨迹和图像采集率的粗糙程度。这种概念提供了类似的灵活性，因为可以应用已知的电磁驱动 MPI 系统中的交变磁场和可调节的磁场梯度，因此为系统的扩展提供了很大的潜力。我们提出了一种 Halbach 阵列的布置的想法，以及如何计算产生的磁场。提供了一个示例几何形状的模拟，以显示所提出的设置的潜力。
